Review of Reported SAR Values in MRI: Current Status and Historical Trends

Purpose: Although MRI is generally considered a very safe imaging modality, potential risks do exist for RF heating during the patient imaging studies and there have been reported skin burn incidents and cases of patient discomforts due to RF heating. RF heating-related safety issues have become more relevant as increasing numbers of high-field (3.0 Tesla or higher) MRI systems are being installed and used in clinical settings. In this study, we reviewed the SAR values on the spine MRI exams over the past few years at our institution and we studied the over-all trend of SAR values and their correlations with patient size (weight).

Methods:With IRB approval, we selected total of 36,051 MRI scans of the spine, dating from September 2005 to June 2012, from the EMR archive at our institution. For each scan sequence, DICOM header information such as SAR value, body weight, scan date, scanner ID, software version are extracted using a MATLAB program developed in-house. The header information was exported to Microsoft Excel for further analysis.

Results:Most of the scans performed on 1.5T scanners have SAR values less than 2.5W/kg while all the 3T scans have reported SAR values less than 3W/kg. However, there are some scans with SAR values above 4W/kg. Additionally, we noticed a gradual upward trend in the SAR values as well as some inconsistencies in the correlations of the reported SAR values to patient weight.

Conclusion:The survey results suggest the need for clinical user involvement in the validation and monitoring of the SAR values. Without proper validation, the reported SAR values may not be accurate and even contain errors, making it difficult to accurately assess the SAR values at the hotspots in patient scans.